The invention relates to a chassis for mounting component units in an electric switch cabinet for elevators and escalators.
For control of electric elevators and escalators, there are required electric control means that are usually accommodated in control or switch cabinets installed in a machine room or hoistway in a building or in an escalator or moving steps. Such switch cabinets conventionally have a sheet metal housing having attached thereto component units, for example, circuit boards, relays, capacitors, transformers etc., by means of frame parts, screws, spacer bolts, brackets etc. One thus arrives at a large amount of parts. It is quite cost-intensive and time-consuming to manufacture all necessary parts, to mount and assemble them and to disassemble them again for maintenance, repair or recycling purposes.
DE 36 12 511 A discloses a distribution cabinet comprising a housing and a component carrier inserted in the housing. The housing comprises a rigid frame consisting of square metal sections and having vertical supports and horizontal rails as well as struts extending along the housing edges. A bottom part, a cover part and side parts of the housing are formed by shaped parts of rigid expanded plastics material and are provided with mounting blocks for mounting the apparatus carrier and with reinforcing ribs. The component carrier has rails for attachment of electrical instruments and equipment. Such a distribution cabinet consists of a plurality of individual components that have to be connected to each other by connecting members and is relatively heavy.
For heavyweight components, such as e.g. transformers or filters, there is a particularly high risk of damage, for instance in the form of broken bolts, screws, anchorages, etc., as a result of vibrations or shocks during transport. Switch cabinets for elevators and escalators furthermore contain noise generating components, such as power switches and relays. Thus, sound-absorbing materials must additionally be accommodated in such a switch cabinet.
It is known from U.S. Pat. No. 5,644,472 A to reduce the assembly cost for desktop computers by inserting individual components of such a computer, such as the main board along with the processor, the fixed disk and the fan, into recesses matched to the shape thereof which are formed in a carrier of foamed urethane material composed of an upper carrier part and a lower carrier part, to thereby maintain the components in their desired positions. Although these components are first held in positive or form-locking manner by the foamed urethane material, it may happen due to vibrations or shocks during transport or during operation of such a desktop computer that the receiving recesses for the individual components are undesirably increased since the foamed urethane material does not have a sufficient resetting force with respect to compression forces, so that deformations of the receiving recesses as a result of vibration and/or shock forces are permanent. This may be counteracted according to the reference, by attaching some or all of the components accommodated in the carrier to the carrier by means of fastening elements such as screws, brackets etc. However, this in turn causes a corresponding increase in manufacturing and mounting cost.
It is known from DE 91 16 755 U1 and the corresponding U.S. Pat. No. 5,473,507 A to make such a carrier for a computer or a measuring apparatus of expanded polypropylene (EPP), a material with high stability in shape and elastic resetting force with respect to compression. Individual components of the computer, such as in particular a fan, a fixed disc, a main board, a loudspeaker and capacitors, are each inserted in a receiving cavity of the carrier that is closely matched to the outer shape of the particular component. Due to the high resetting force of the plastics material used and the snug fit of the individual components, the components are permanently retained in their position. There are thus no additional fastening elements provided, so that an overall reduction in manufacturing and mounting cost is obtained.
However, such carriers are designed for receipt of comparatively light-weight computer components which remain identical in their outer shape for various computer models, and are not suited without further ado as carriers for elevator and escalator switch cabinets that must carry components or components units that are not only relatively heavy in part, but which in part may also have quite different shapes and/or may be provided in different numbers, depending on the particular model and intended application of the particular switch cabinet. If the conception of the above-mentioned carriers were used for computers for elevator and escalator switch cabinets, a matched shaped plastics part of its own would have to be produced for each switch cabinet model, which would require a corresponding number of injection molds. In the light of the comparatively low number of pieces per switch cabinet model for escalators and elevators, as compared with mass-produced apparatus like computers, this would constitute an unbearable cost expenditure.
It is the object of the invention to make available a chassis of the type indicated at the outset, through which the manufacturing and mounting costs for elevator and escalator switch cabinets can be reduced by making use of the afore-mentioned conception for carriers of computer components, while simultaneously reducing the possibility of damages, and improving both noise attenuation as well as usability for various switch cabinet models.
A chassis of the type according to the invention comprises a shaped part (molded part) serving as main supporting member, which is composed with a plastics material with lasting resetting force with respect to compression and is provided with at least one receiving recess for receiving a component unit of a first type in substantially positive snug fitting or form-locking manner. In addition thereto, a chassis of the type according to the invention is provided with at least one mounting rail serving as auxiliary supporting member and anchored in the shaped part, said mounting rail, at least over a predetermined partial length thereof, being accessible in a free space of the shaped part for mounting at least one component unit of a second type to said mounting rail, with said free space being designed and dimensioned such that such component units of the second type can be received in different numbers, shapes and sizes.
In an embodiment of the invention, the shaped part consists of expanded polypropylene (EPP). However, any other plastics material with stability in shape and sufficient lasting resetting force as regards compression may be used as well. Alternative materials are, for instance, polyurethane and polyethylene. Plastics materials are preferred that can be injection-molded in an injection mold also as larger shaped parts.
Each of the component units of a first type has associated therewith a receiving recess of its own of the chassis, which is closely matched to the outer shape of the respective component unit and receives this component unit to a predetermined insertion depth. Preferably, the respective receiving recess is dimensioned such that the associated component unit is received therein in a press fit. Due to the high resetting force of the plastics material used, a holding force is exerted on the respective component unit such that it is permanently held in its position. The component units of the first type merely need to be inserted in the receiving recesses provided therefor, so that an overall reduction of the manufacturing and mounting expenditure is obtained. For such component units, in the event they are too heavy to be still safely held in their receiving recesses by the resetting force of the plastics material of the shaped part also in case of tipping of the chassis, there may be provided additional fastening elements for safely fixing such component units.
Due to the fact that supporting rails, supporting frames and other supporting members of conventional switch cabinets for elevators, escalators and moving steps have all been replaced by a shaped part of plastics material, there chassis according to the present invention achieves considerable noise attenuation as compared to the prior art. This is enhanced still further if noise-generating component units, in the receiving recesses thereof, are surrounded in part by the noise-absorbing plastics material of the shaped part.
In a plastic shaped part as used for the chassis according to the invention, cooling air can be directed and channelled more effectively than in conventional switch cabinets. The cooling air can be better directed towards component units requiring cooling, so that a reduced cooling capacity is sufficient or an increased cooling efficiency can be obtained.
In a preferred embodiment of the invention, the chassis is open at least in the upward direction. The individual component units thus are not enclosed on all sides, but project upwardly from the respectively associated receiving recesses providing especially good accessibility in the event of maintenance or repair as well as facilitated cooling are rendered possible.
Due to the fact that the component units of the second type are not received in a receiving recess designed to receive the same in a snug or form locking manner, but are received in the free space of the shaped part that is not configured on the shape thereof, increased flexibility to the effect is obtained that mutually different circuit arrangements can be arranged in a specific chassis, for example circuit arrangements with different power demands having power components in different numbers and/or of different shape. Those component units that are identical for all different circuit arrangements (components units of the first type) are received in a form-locking manner by receiving recesses that are matched to the outer configuration thereof Those component units which for the different circuit arrangements are of different shape or size or are present in different numbers (component units of the second type), are accommodated in one or more free spaces of the shaped part. The result of this embodiment according to the present invention is that it is not necessary to manufacture a shaped part of its own for receiving each circuit arrangement of different type, but that identical shaped parts may be used for a larger number of different circuit arrangements. This leads to a considerable reduction in manufacturing costs as a larger number of shaped parts can be produced using one injection mold.
Due to the fact that the component units of the second type are not held with the aid of the resetting force of the plastics material of the shaped part, the chassis according to the present invention provides at least one mounting rail that is anchored in the shaped part and is accessible in the region of the free space for mounting one or more component units of the second type.
The component units of the second type thus in the end are carried by the shaped part of the chassis as well, however not directly, like the component units of the first type, but by means of the mounting rail.
A further advantage in using a mounting rail consists in that the load of a component unit mounted to the mounting rail, by means of the supporting rail, can be introduced into areas of the shaped part which, due to the overall shape of the shaped part, are capable of supporting particularly high loads, possibly to a much higher extent than those areas of the shaped part adjacent the component unit mounted to the supporting rail.
Preferred as mounting rails are rails that have become widely available and standard in switch cabinet construction. Particularly preferred are so-called top hat rails according to European standards EN 50022 and EN 50045 as well as so-called C-rails according to EN 50035. However, other constructions may be used as well, such as, for example, perforated rails and perforated angle pieces, threaded hole rails and threaded hole angle pieces as well as profiled rails of other types that serve for installation of components.
A top hat rail is an approximately U-shaped rail having a rail bottom with a rail side wall upstanding from each of the two longitudinal sides thereof, the free end of each side wall being provided with a rail edge projecting outwardly from the respective rail side wall and serving for attachment of component units with fasting elements of complementary design. In preferred embodiments of the invention, the mounting rail consists of metal. However, it may also be made of ceramics or plastics material of sufficient hardness, dimensional stability and breaking strength.
In a further embodiment of the invention, the mounting rail is held in the shaped part so as to be longitudinally slidable to provide for easier insertability of the mounting rail in the shaped part and easier assembly of one or more component units of the second type in the free space at the mounting rail. The longitudinal slidability of the mounting rail in both of its longitudinal sliding directions may be unlimited, in particular if the chassis, in the state of use thereof, is received in an enclosing casing or switch cabinet housing that limits the longitudinal sliding motion of the mounting rail in both directions. A limitation of the longitudinal slidability of the mounting rail, at least in one of its longitudinal sliding directions, may also be obtained by a longitudinal sliding motion stopper formed in the shaped part.
In a still further embodiment of the invention, a rail anchoring element is releasably mounted in at least one longitudinal location of the mounting rail, with said rail anchoring element being received in an anchoring receiving opening of the shaped part of approximately matching shape. The rail anchoring element, for example, is an about disk-shaped plastic part that is slid onto the mounting rail and surrounds in particularly the outer edges thereof so that these cannot cut into the plastics material of the shaped part. Moreover, the rail anchoring element can be provided with a disk area that is much larger than the cross-sectional area of the mounting rail, whereby the pressing force exerted by the mounting rail can be distributed via the rail anchoring element to a considerably larger area of the shaped part than in case of the direct receipt of the mounting rail by the shaped part.
In case the chassis is to accommodate component units which, for example with regard to their weight, should be secured in particular manner against the effects of vibrations, shocks and tipping of the chassis, such as during transport thereof, an embodiment of the invention provides for the arrangement of at least one dowel-like fastening element in a surface of the shaped part, at which such a component unit can be fixed, either directly or by means of a holding device between the component unit and the dowel-like fastening element. As such a dowel-like fastening element, there is suitable in particular a dowel with large radial anchoring area that was developed for sandwich type plaster boards and is available e.g. from the company Fischer (Arthur Fischer GmbH and Co. KG, Weinhalde 14-18, D-72178 Waldauchtal, Germany) under the designation GK. By means of this anchoring area, tensile forces exerted on the dowel in case of acceleration forces of the type mentioned, are converted primarily to compression forces with respect to the plastics material of the shaped part. Thus, the plastics material of the shaped part is subject predominantly to compression forces which the shaped part plastics material of the type preferred can withstand to a much higher extent than tensile forces.
In a chassis according to the invention, electric connecting cables must be accommodated for electrically interconnecting component units and/or apparatus located inside the chassis and/or outside the chassis. In a preferred embodiment of the invention such cables are housed in one or more cable ducts that are molded in the shaped part. In the event that the chassis accommodates component units in different numbers and/or of different power categories, electric connecting cables in corresponding numbers and/or of corresponding diameter must be accommodated as well. At least one cable duct of the chassis thus is preferably designed such that it is capable of accommodating different numbers of cables and/or cables of different thicknesses. In a particularly preferred embodiment, at least one cable duct is provided with at least one strain relief means. The strain relief may be formed by strain-relieving constrictions of the respective cable duct, into which at least one cable is urged. Along the cable duct, there may also be provided several strain-relieving constrictions so as to ensure that cables of short length are supported by at least one strain-relieving location, and that cables of greater length experience strain-relief at several locations along their longitudinal extension.
Particularly high strain relief for a cable to be inserted in the chassis is obtained in a still further embodiment of the invention in which the cable is placed in the injection mold for molding the shaped part and, during injection molding of the shaped part, is embedded in the shaped part plastics material in strain-relieving manner.
In a still further embodiment of the invention the shaped part has at least one fan receiving recess for receipt of at least one motor-driven fan for ventilating a ventilation space of the shaped part. The ventilation space is constituted in essence by the entire empty space of the shaped part that is not filled with shaped part plastics material and component units inserted in the shaped part.
Unlike in traditional switch cabinets in which cooling air circulates in substantially uncontrolled manner through the entire switch cabinet interior, a chassis according to the invention, due to the configuration of the shaped part, can ensure purposeful cooling air control and cooling air distribution. By corresponding design of the empty space of the shaped part, the cooling air may be directed in more purposeful manner to component units with a higher need of cooling.
Due to the fact that as in a conventional switch cabinet in which the entire interior of the switch cabinet constitutes the ventilation space, the chassis according to the present invention uses only the empty space of the shaped part, which can be designed purposefully, so that a comparatively low power fan is sufficient to generate a positive ventilation pressure which prevents the ingress of dust or other dirt particles into the interior of the switch cabinet, with the air sucked in by the fan being filtered. The effect achieved thereby is that only filtered air reaches the interior of the switch cabinet and unfiltered air cannot enter into the switch cabinet interior via slots, crannies and other openings which cannot be avoided in switch cabinet housings of the usual kind. The danger of contamination of the switch cabinet interior due to unfiltered air is particularly high for elevator switch cabinets and escalator switch cabinets since such switch cabinets are arranged in machine rooms or hoistways and escalators, which usually are not, or only with difficulty, accessible for regular overall cleaning, so that much dust and dirt accumulates in such spaces in the course of time.
In practical application, a chassis according to the invention is surrounded by an enclosing housing or enclosure. The latter may be formed in particular by a switch cabinet housing accommodating at least one chassis according to the invention. This enclosure may also be designed such that it limits the longitudinal slidability of a mounting rail inserted in the shaped part of the respective chassis in at least one longitudinal sliding direction.
In an embodiment of the invention in which a plurality of chassis of the type according to the invention are accommodated in a switch cabinet, each chassis would constitute a module adapted to be separately inserted into and removed from the switch cabinet. Preferably, each module has at least one fan of its own, with the overall ventilation system being designed such that an excess ventilation pressure is created in the switch cabinet.
In a particularly preferred embodiment of a switch cabinet according to the invention, the switch cabinet housing and at least one chassis are dimensioned such that the chassis is accommodated in the switch cabinet housing in a press fit. This has the effect that the side walls of the switch cabinet have to bear only the weight of the one chassis loaded and the switch cabinet cover, but need not have lateral stability of their own, since the latter is given to them by the one chassis accommodated in a press fit.
By way of comparison, a typical prior art elevator switch cabinet comprises a switch cabinet housing having a rear wall with a thickness of 3 mm, to which a transformer and other heavy parts must be bolted or otherwise firmly secured. The remaining walls of this switch cabinet housing have a sheet metal thickness of 1 to 1.5 mm. This switch cabinet housing has a weight of approximately 50 kg.
In a comparative embodiment of an elevator switch cabinet used with a chassis according to the present invention, a sheet-metal thickness of 0.8 mm is sufficient for all walls of the switch cabinet housing, thereby reducing the overall weight of the switch cabinet housing to 15 kg.
The invention can be utilized also with frequency converters for which power semiconductor components of high voltage compatibility and/or performance are employed. A frequency converter according to the invention comprises a frequency converter housing accommodating at least one chassis having the features of a chassis according to the invention as claimed and described hereinbefore.
The invention as well as further objective aspects and advantages of the invention will now be elucidated in more detail by way of embodiments. These relate to a switch cabinet for elevators or escalators which contains three modules, namely a control module, a frequency converter module (hereinafter referred to as drive module) and a filter module, with one chassis according to the invention each.